The Duke appears on the cover of the June issue of Attitude magazine. Photograph: Attitude/ PA
A number of previous covering stars, including the Olympic diver Tom Daley and pop starring Harry Judd, of McFly, have appeared topless but the comedian, writer and broadcaster, Stephen Fry, and singer Gary Barlow, seem, like William, fully clothed.
The cover came about after the Duke of Cambridge invited Attitude to bring members of the LGBT+ community to Kensington Palace to hear their experiences of bully and discuss the impact on mental health.
William, along with the Duchess of Cambridge and Prince Harry, is leading the Heads Together campaign, which aims to end stigma around mental health.
He told Attitude: No one should be bullied for their sexuality or any other reason and no one should have to put up with the various kinds of abhor that these young people have endured in their lives. The young homosexual, lesbian and transgender individuals I fulfilled through Attitude are truly brave to speak out and to give hope to people who are going through terrible bullying right now. Their sense of strength and optimism should devote us all encouragement to stand up to bullying wherever we see it.
He advised anyone who was being bullied for their sexuality to contact someone whom they could trust, whether a friend, teacher or other adult, or a service such as Childline or the Diana Award. You should be proud of the person you are and you have nothing to be ashamed of, the prince said.
According to research 33.9% of young LGB people have made at least one suicide attempt, compared with 17.9% of young straight people, while 48.1% of trans young people have attempted suicide.
Matthew Todd, editor of Attitude, said: During my time as editor I have met mothers whose child has taken or lost their life after being bullied for being LGBT+ or only perceived to be LGBT. I am very happy that the future king of the UK agrees this must stop.
The issue of Attitude magazine went to press on 8 June, just days before the killing of 49 people at a gay club in Orlando, in the US. On Tuesday, William and Kate signed a book of condolences at the American embassy for victims of the massacre.
The magazine said: Such violence does not exist in a vacuum but snowballs from fanaticism and bullying that begins in classrooms, too often comes from legislators or religious leaders, and is often not treated with respect by the media.
The print edition featuring William will be in shops next Wednesday.
This article was amended on on 15 June to correct the fact the Prince William is second-in-line to the throne rather than heir.